U.S. patent application number 12/396679 was filed with the patent office on 2010-05-06 for fast response failure mode control methodology for a hybrid vehicle having an electric machine.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Gerald T. Fattic, James E. Walters.
Application Number | 20100110594 12/396679 |
Document ID | / |
Family ID | 42061041 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100110594 |
Kind Code |
A1 |
Walters; James E. ; et
al. |
May 6, 2010 |
FAST RESPONSE FAILURE MODE CONTROL METHODOLOGY FOR A HYBRID VEHICLE
HAVING AN ELECTRIC MACHINE
Abstract
A control methodology for an engine-driven electric machine of a
hybrid vehicle electrical system for enabling continued operation
of the vehicle electrical system under failure mode conditions that
require or result in disconnection of the battery pack from the
electrical system. At the onset of a fault condition requiring
battery disconnection, the electric machine is controlled to drive
the battery pack current toward zero before disconnecting the
battery pack. Once the battery pack is disconnected, whether by
relay or fuse, the electric machine is controlled to maintain the
bus voltage of the electrical system at a specified value. In both
operating modes, the electric machine is controlled based on a
synchronous vector current command that is determined directly as a
function of the control objective (zero battery pack current or
maintaining bus voltage) for improved response time compared to a
traditional torque-based control.
Inventors: |
Walters; James E.; (Carmel,
IN) ; Fattic; Gerald T.; (Fishers, IN) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC;LEGAL STAFF - M/C 483-400-402
5725 DELPHI DRIVE, PO BOX 5052
TROY
MI
48007
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
TROY
MI
|
Family ID: |
42061041 |
Appl. No.: |
12/396679 |
Filed: |
March 3, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12290974 |
Nov 5, 2008 |
|
|
|
12396679 |
|
|
|
|
Current U.S.
Class: |
361/52 ;
903/930 |
Current CPC
Class: |
B60W 10/28 20130101;
B60W 10/08 20130101; B60K 6/485 20130101; B60L 3/0069 20130101;
B60L 3/00 20130101; B60W 10/26 20130101; B60W 20/00 20130101; B60K
6/48 20130101; Y02T 10/70 20130101; B60K 6/46 20130101; B60L
2220/14 20130101; Y02T 10/62 20130101; B60L 3/0046 20130101; B60L
3/12 20130101; B60W 20/50 20130101; Y02T 10/64 20130101; B60K
2006/4833 20130101; B60L 50/16 20190201; B60L 3/0092 20130101; B60L
15/025 20130101; Y02T 10/7072 20130101; B60L 2220/18 20130101; B60L
3/04 20130101 |
Class at
Publication: |
361/52 ;
903/930 |
International
Class: |
H02H 7/08 20060101
H02H007/08 |
Claims
1. A control methodology for a hybrid vehicle electrical system
including one or more electrical loads, an engine-driven AC
electric machine operable as a generator for supplying power to
said electrical loads via a high voltage bus, and a high voltage
battery pack coupled to the high voltage bus by a power coupler
that can open to disconnect the battery pack from the high voltage
bus under fault conditions, the control methodology comprising the
steps of: initiating a fault mode control of said electric machine
in response to a detected disconnection of said battery pack from
said electrical system by said power coupler, including directly
calculating vector current commands for said electric machine based
on a deviation of an operating voltage of said high voltage bus
from a target voltage, and controlling said electric machine based
on the calculated vector current commands to maintain the operating
voltage of said high voltage bus at said target value.
2. The control methodology of claim 1, where the power coupler
includes a fuse that opens due to an over-current condition, the
control methodology including the steps of: detecting opening of
said fuse; and initiating said fault mode control in response to
the detection of fuse opening.
3. The control methodology of claim 2, including the step of:
detecting opening of said fuse based on a comparison of the
operating voltage of said high voltage bus and a voltage of said
battery pack.
4. The control methodology of claim 1, including the steps of:
calculating a q-axis vector current command for said electric
machine based on the deviation of the operating voltage of said
high voltage bus from the target voltage; and calculating a d-axis
vector current command for said electric machine based on a measure
of q-axis current in said electric machine.
5. The control methodology of claim 1, where the power coupler
includes a relay that can be opened to disconnect the battery pack
from the high voltage bus, the control methodology including the
steps of: overriding a normal control of said electric machine in
response to a fault condition requiring disconnection of the
battery pack from the high voltage bus by directly calculating
vector current commands for said electric machine based on a
deviation of a current of said battery pack from zero current, and
controlling said electric machine based on the calculated vector
current commands to drive the current of said battery pack toward
zero; and activating the relay to disconnect the battery pack from
the high voltage bus when the current of said battery pack falls
below a threshold current.
6. The control methodology of claim 5, including the steps of:
calculating a q-axis vector current command for said electric
machine based on the deviation of the current of said battery pack
from zero current; and calculating a d-axis vector current command
for said electric machine based on a measure of q-axis current in
said electric machine.
Description
RELATED APPLICATIONS
[0001] The present invention is a continuation-in-part of
co-pending U.S. patent application Ser. No. 12/290,974, filed Nov.
5, 2008, and assigned to the assignee of the present patent
application.
FIELD OF THE INVENTION
[0002] The present invention is directed to a failure-mode battery
disconnect method for a hybrid vehicle electrical system including
a high voltage battery pack and an engine-driven electric machine
operable in generating and motoring modes, and more particularly to
a control method for the electric machine that permits continued
operation of the engine and electric machine after the battery pack
is disconnected from the electrical system.
BACKGROUND OF THE INVENTION
[0003] The fuel efficiency of a motor vehicle can be considerably
enhanced with a hybrid system including an electric machine coupled
to the engine, a high voltage battery pack, and a power electronics
system for interconnecting the electric machine, the battery pack
and the electrical loads of the vehicle. The electric machine is
operable in a generating mode to charge the battery pack and supply
power to various electrical loads, and in a motoring mode to crank
the engine and to augment the engine power output. Various drive
arrangements can be used to propel the vehicle. For example, the
engine can be coupled to the drive wheels through a conventional
drivetrain, and/or one or more electric propulsion motors can be
used.
[0004] FIG. 1 illustrates an example of a hybrid vehicle system
including an engine 10 that is mechanically coupled to a set of
drive wheels 12 through a transmission (T) 14 and differential
gearset (DG) 16. The hybrid vehicle system includes an AC electric
machine 18, a main 120-volt battery pack 20, and a power conversion
system 22. The electric machine 18 is selectively operable in
generating and motoring modes, and is mechanically coupled to the
engine 10, either directly or by way of a drive belt. The power
conversion system 22 includes a high voltage DC bus 24, one or more
bus capacitors 26 for maintaining the bus voltage, a power coupler
28 coupling the positive side of high voltage bus 24 to the battery
pack 20, an inverter 30 coupling high voltage bus 24 to the
electric machine 18, a DC-to-DC converter 32 coupling high voltage
bus 24 to a low voltage DC bus 34, and a Power Control Unit (PCU)
36 for controlling the operation of inverter 30 and DC-to-DC
converter 32. The power coupler 28 may be implemented with a fuse,
with a controlled element such as a relay, or with a fuse in series
with a relay; and in mechanizations where the power coupler 28
includes a relay, its on/off state is controlled by PCU 36 as
indicated in FIG. 1. The low voltage DC bus 34 is used to supply
power to various 12-volt electrical loads 38 of the vehicle, and an
auxiliary 12-volt storage battery 40 is coupled to the low voltage
bus 34 for maintaining the bus voltage and temporarily supplying
power to the loads 38 in the event of a system failure.
[0005] In mechanizations where the power coupler 28 includes a
relay or other controlled element, the PCU 36 is programmed to open
the relay when a failure mode requiring battery pack disconnection
is detected. In order to minimize the current that the relay must
break and to prevent load-dump transient voltages, the PCU 36
ordinarily powers down the inverter 30 and DC-to-DC converter 32
prior to opening the relay. However, once the relay is open and the
battery pack 20 is off-line, there is insufficient reserve
electrical power in the bus capacitor 26 to re-activate the
electric machine 18, and the only source of power for the
electrical loads 38 is the auxiliary storage battery 40. A similar
situation occurs in mechanizations where the power coupler 28
includes a fuse that opens in response to an over-current
condition, except that the inverter current automatically collapses
when the fuse opens. In either case, the battery pack disconnection
significantly limits the post-failure range of the vehicle because
certain electrical loads such as the engine ignition system are
required for continued operation of engine 10, and the auxiliary
battery 40 can only power such loads for a limited period of time.
Accordingly, what is needed is a way of utilizing the generating
capability of the electric machine 18 to power the vehicle
following a controlled or uncontrolled disconnection of battery
pack 20 from the high voltage bus 24.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to an improved control
methodology for an engine-driven electric machine of a hybrid
vehicle electrical system for enabling continued operation of the
vehicle electrical system under failure mode conditions that
require or result in disconnection of the battery pack from the
electrical system. At the onset of a failure mode condition
requiring disconnection of the battery pack in systems including a
controlled power coupler such as a relay, the electric machine is
operated as a generator and is controlled in accordance with a
first mode of operation that drives the battery pack current toward
zero. When the battery pack current falls below a near-zero
threshold, the power coupler is activated to disconnect the battery
pack from the electrical system. Once the battery pack is
disconnected from the electrical system, whether by relay or fuse,
the electric machine is controlled according to a second mode of
operation that maintains the bus voltage of the electrical system
at a specified value. In both operating modes, the electric machine
is controlled based on a synchronous vector current command that is
determined directly as a function of the control objective (zero
battery pack current or maintaining bus voltage) for improved
response time compared to a traditional torque-based control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram of an exemplary hybrid vehicle
electrical system and powertrain, including an engine, a high
voltage battery pack, a power coupler, an inverter, an
engine-driven electric machine operable in generating and motoring
modes, and a microprocessor-based Power Control Unit;
[0008] FIG. 2 is a block diagram of the Power Control Unit, the
inverter and the electric machine of FIG. 1;
[0009] FIG. 3 is flow diagram representing a control methodology
according to this invention that is implemented by the Power
Control Unit of FIG. 1 for a system in which the power coupler
includes only a fuse; and
[0010] FIG. 4 is flow diagram representing a control methodology
according to this invention that is implemented by the Power
Control Unit of FIG. 1 for a system in which the power coupler
includes both a fuse and a relay.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] While the method of the present invention is disclosed
herein in the context of the exemplary hybrid vehicle electrical
system and powertrain of FIG. 1, it should be understood that the
described method is applicable to any hybrid vehicle electrical
system including a battery pack and an engine-driven electric
machine. Virtually all hybrid vehicle electrical systems include a
battery pack for storing electrical energy and an engine-driven
electric machine selectively operable in a generating mode to
charge the battery pack and supply power to various electrical
loads, and in a motoring mode to crank the engine and to augment
the engine power output. And in all such configurations, there is
the possibility of a failure mode condition that requires or will
result in disconnection of the battery pack from the vehicle
electrical system. If a contactor device such as a relay is used to
disconnect the battery pack, the battery pack current is first
reduced to ensure safe and reliable current interruption. But the
conventional approach of powering down the inverter 30 and DC-to-DC
converter 32 to reduce the battery pack current discharges the bus
capacitor 26, leaving insufficient reserve electrical power to
re-activate the electric machine 18. And of course, the same thing
can happen when the battery pack disconnect occurs due to opening
of an in-line fuse due to an over-current condition. In both cases,
the auxiliary storage battery 40 is then the only source of power
for the electrical loads 38, and the vehicle range will be
substantially curtailed, particularly in hybrid configurations that
utilize electric propulsion motors.
[0012] The method of the present invention overcomes the problem
outlined above by utilizing the generating capability of the
electric machine 18 to enable continued vehicle operation after the
battery pack 20 is disconnected from the high voltage bus 24. In
mechanizations where the power coupler 28 includes a relay, the
battery pack current is first minimized by operating the electric
machine 18 with the control objective of driving the battery pack
current substantially to zero. And once the battery pack 20 is
safely disconnected, whether by relay or fuse, the electric machine
18 is operated with the control objective of maintaining the high
voltage bus 24 at a desired voltage to enable continued normal
operation of the vehicle until the engine 10 is turned off.
[0013] An important aspect of the present invention is that under
fault conditions that require or result in battery pack
disconnection, the electric machine control for enabling continued
operation of the vehicle is carried out by bypassing the usual
torque-based control, and directly determining the synchronous
vector current required to achieve the control objective. The
control is described herein in the context of an AC induction
machine, but is also applicable synchronous reluctance and
permanent magnet AC electric machines. The regulated current to the
machine can be broken into direct and quadrature vector components.
In a basic system, the quadrature or q-axis component (Iqs) is used
to quickly control the produced torque or generating power, and the
direct or d-axis component (Ids) is used to control the flux level
of the machine, which changes at a slower rate. The two current
vectors interact to produce torque equal to
[(3/2)*(P/2)*(Lm.sup.2/Lr)*Iqs*Ids], where P is the pole number of
the machine, Lm is the magnetizing inductance, and Lr is the rotor
inductance.
[0014] When the control objective is reducing the battery current
to zero, while continuing to provide power to electrical loads 38
via DC-to-DC converter 32, the synchronous current vector command
Iqs-CMD is determined as follows:
Iqs.sub.--CMD=(0-I.sub.--BP)*[k.sub.p+(k.sub.i/s)] (1)
where I_BP is the battery pack current and the term
[k.sub.p+(k.sub.i/s)] denotes a generic proportional-plus-integral
control function. In other words, the current vector command
Iqs_CMD is directly determined as a function of the deviation of
I_BP from the target value of zero current. When the control
objective is maintaining the HV bus voltage at a target value
V_BUS_TAR, the synchronous current vector command Iqs_CMD is
determined as follows:
Iqs.sub.--CMD=-1*(V.sub.--BUS.sub.--TAR-HV.sub.--BUS)*[k.sub.p+(k.sub.i/-
s)] (2)
where HV_BUS is the voltage of high voltage bus 24. In this case,
the current vector command Iqs_CMD is directly determined as a
proportional-plus-integral function of deviation of HV_BUS from the
target value V_BUS_TAR. In both control modes, the commanded value
for the d-axis component of the stator current, or Ids_CMD, is
preferably determined by table look-up as a function of the actual
(measured) value of Iqs and/or machine speed, but it will be
appreciated that other flux control strategies could alternatively
be utilized.
[0015] The block diagram of FIG. 2 illustrates the above-described
control scheme in the context of an induction machine 18. Referring
to FIG. 2, the inverter 30 and electric machine 18 correspond to
the same components of FIG. 1, and the remaining items represent
either sensors or the relevant functions performed by PCU 36 of
FIG. 1. The Control Logic block 50 determines the q-axis and d-axis
synchronous current commands Iqs_CMD and Ids_CMD in response to
various inputs generally identified in FIG. 2. The reference
numeral 42 designates a number of system-related inputs such as
V_BP (battery pack voltage), I_BP and HV_BUS, the reference numeral
44 designates a machine speed input (Speed) produced by Angle
Processing block 52, and the reference numeral 74 represents a
q-axis current feedback signal Iqs_FB produced by Coordinate
Transform and Rotation (CTR) block 56. The flow diagram of FIG. 3
describes how Control Logic block 50 determines Iqs_CMD and Ids_CMD
for a system in which the power coupler 28 is a fuse, whereas the
flow diagram FIG. 4 describes how Control Logic block 50 determines
Iqs_CMD and Ids_CMD for a system in which the power coupler 28 is a
relay, or a fuse in series with a relay.
[0016] The synchronous current commands Iqs_CMD and Ids_CMD
developed by Control Logic block 50 are applied as inputs to the
Current Controller 54, which also receives feedback current values
Iqs_FB and Ids_FB from Coordinate Transform and Rotation block 56
via lines 74 and 76. Current Controller 54 develops a q-axis
voltage command Vq based on the deviation of Iqs_FB from Iqs_CMD,
and a d-axis voltage command Vd based on the deviation of Ids_FB
from Ids_CMD. In both cases, the control function preferably
includes both proportional and integral control terms. The voltage
commands Vq_CMD and Vd_CMD, like the current commands Iqs_CMD and
Ids_CMD, are based on frame of reference that is synchronous with
the d-axis rotor flux of the electric machine 18, and the
Coordinate Transform (CTX) block 58 transforms (rotates) the
voltage commands Vq_CMD and Vd_CMD to a stationary reference frame,
using a synchronous rotor phase angle input .theta.sync provided by
blocks 52, 66 and 68 (described below) on line 70. The transformed
voltage commands are applied as control inputs to PWM Generator 60,
which in turn, correspondingly activates the switching elements of
inverter 30.
[0017] As mentioned above, the Angle Processing block 52 develops
the speed input on line 44, and in conjunction with blocks 66 and
68, the synchronous rotor phase angle input .theta.sync on line 70.
Angle Processing block 52 is responsive to the output of an output
shaft (i.e., rotor) rotation encoder, as represented by the broken
line 62. Angle Processing block 52 determines the machine speed
(i.e., the speed input on line 44) as the time rate of change in
rotor position, and the rotor position .theta.rotor in electrical
degrees. Since the machine 18 is an induction machine in the
illustrated embodiment, the synchronous phase angle input
.theta.sync is determined according to the sum of .theta.rotor and
a slip angle .theta.slip provided by Slip Angle Calculator 66. In
embodiments where the machine 18 is a synchronous reluctance
machine or a permanent magnet AC machine, the determined value of
.theta.rotor is used for .theta.sync.
[0018] As also mentioned above, the Coordinate Transform and
Rotation block 56 provides feedback currents Iqs_FB and Ids_FB to
Current Controller 54 on lines 74 and 76. The feedback currents
Iqs_FB and Ids_FB are obtained by measuring the phase currents Ia
and Ib of electric machine 18 using the current sensors 72,
converting the phase currents to corresponding q-axis and d-axis
current vectors, and then transforming the current vectors from a
stationary frame of reference to a frame of reference that is
synchronous with the d-axis rotor flux of the electric machine 18,
using the synchronous phase angle input .theta.sync developed by
blocks 52, 66 and 68.
[0019] The flow diagram of FIG. 3 represents a software routine
carried out by PCU 36 of FIG. 1 for implementing the functionality
of Control Logic block 50 of FIG. 2 for a system in which the power
coupler 28 is a fuse that automatically opens in response to an
over-current fault. Since fuse opening is an uncontrolled event,
the flow diagram blocks 80-86 pertain to fuse-opening detection.
Prior to detection of a fuse-opening event, block 80 is answered in
the negative and blocks 82-84 are executed to determine if a
fuse-opening event has occurred. Block 82 computes a voltage
difference V_DIFF between the battery pack voltage V_BP and the
voltage HV_BUS across high voltage bus 24. If the voltage
difference V_DIFF exceeds a specified threshold voltage such as 5
VDC, block 84 is answered in the affirmative, and block 86 sets a
flag to indicate that a fuse-opening event has been detected. In
that case, block 80 will thereafter be answered in the affirmative,
and blocks 82-86 will be skipped as indicated. Also, it will be
understood that fuse opening may be detected using other readily
available parameters such as the value or rate of change in I_BP
and/or HV_BUS.
[0020] Prior to the detection of a fuse-opening event by block 84,
the electric machine 18 is operated normally, as indicated by
blocks 88 and 98. This involves determining a desired torque TQ_DES
for electric machine 18 based on vehicle requirements (VRs),
calculating q-axis and d-axis current vector commands Iqs_CMD and
Ids_CMD corresponding to TQ_DES, and outputting Iqs_CMD and Ids_CMD
to the Current Controller 54 of FIG. 2. In the motoring mode,
TQ_DES represents the desired torque output of machine 18; and in
the generating mode, TQ_DES represents a load torque that is borne
by engine 10 to generate electrical power for the power conversion
system 22.
[0021] Controlling electric machine 18 as a function of desired
torque as described in reference to blocks 88 and 98 provides
sufficiently fast response for normal operation of the vehicle, but
may not be sufficiently fast to prevent the bus capacitance 26 from
discharging when the fuse of power coupler 28 opens due to an
over-current condition. For this reason, the normal torque-based
control of block 88 is by-passed when a fuse-opening event is
detected by blocks 80-86. First however, block 90 compares the
machine speed to a threshold speed such as 1000 RPM; if the machine
speed is less than the threshold, there is insufficient generating
capability to proceed, and the control logic is exited, as
indicated by block 92. However, if the machine speed is greater
than the threshold, blocks 94 and 96 are executed to calculate
q-axis and d-axis current vectors Iqs_CMD and Ids_CMD for achieving
the control objective of maintaining HV_BUS at the target value
HV_BUS_TAR. The q-axis current vector Iqs_CMD is calculated based
on the bus voltage error as described above in reference to
equation (2), and the d-axis current vector Ids_CMD is determined
by table look-up as a function of Iqs_FB and the machine speed. And
block 98 then outputs the current vector commands to the Current
Controller 54 of FIG. 2.
[0022] The flow diagram of FIG. 4 represents a software routine
carried out by PCU 36 of FIG. 1 for implementing the functionality
of Control Logic block 50 of FIG. 2 for a system in which the power
coupler 28 is implemented with a relay in series with a fuse that
automatically opens in response to an over-current fault. In
mechanizations where the power coupler 28 includes a relay (or
other controlled disconnect device) but not a fuse, the portions of
the flow diagram pertaining only to fuse-opening detection (i.e.,
blocks 80-86 and 108) are omitted.
[0023] During conditions where relay-based disconnection of the
battery pack 20 is not required, the flow diagram of FIG. 4
operates the same as the flow diagram of FIG. 3. That is,
torque-based normal operation of the machine 18 occurs prior to
detection of a fuse-opening event, and current vector-based
override control of the machine 18 occurs to maintain the HV bus
voltage upon detection of a fuse-opening event. Thus, the reference
numerals designating blocks 80-98 of FIG. 3 are repeated in the
flow diagram of FIG. 4.
[0024] Referring now specifically to FIG. 4, the block 100 is first
executed to determine if the relay is already open. Initially of
course, block 100 will be answered in the negative, resulting in
the execution of fuse-opening detection blocks 80-86 as described
above in reference to the flow diagram of FIG. 3. If the fuse is
not open, block 84 will be answered in the negative, and block 102
is executed to determine if there is a fault condition requiring
disconnection of battery pack 20. If the absence of such a fault
condition, blocks 88 and 98 are executed as described above in
reference to the flow diagram of FIG. 3 to carry out a normal
torque-based control of electric machine 18 based on vehicle
requirements (VRs). However, if battery pack disconnection is
required, block 104 is first executed to determine if the battery
pack current (I_BP) is below a threshold current such as 2 A. If
so, blocks 106 and 108 are executed to open the relay and set a
flag to show the relay status; in subsequently executions of the
routine, block 100 will be answered in the affirmative to skip the
blocks 80-88 and 102-108. However, if I_BP is not below the current
threshold, the remainder of the routine (i.e., beginning at block
90) is first executed to control electric machine 18 to drive the
I_BP substantially to zero.
[0025] The portion of the routine beginning at block 90 is executed
whenever a battery pack disconnect has occurred, or a relay-based
battery pack disconnect is required. The block 90 is first executed
to ensure that the machine speed is sufficiently high, as described
above in respect to the flow diagram of FIG. 3. If not, the system
reverts to a conventional control strategy in which the relay is
opened after shutting down inverter 30 and DC-to-DC converter 32.
Block 110 checks whether the relay is already open, and if it is
not, block 112 is executed to open the relay using the conventional
control strategy. In either event, the control logic routine is
then exited at block 92. However, if the machine speed exceeds the
threshold of block 90, block 114 is executed to determine if fuse
opening has been detected. If so, blocks 94-98 are executed to
operate electric machine 18 to maintain the bus voltage HV_BUS at
the target value HV_BUS_TAR, as described above in respect to the
flow diagram of FIG. 3. If fuse opening has not been detected,
block 116 is executed to determine if the relay is open. If the
relay is not open, blocks 118, 96 and 98 are executed to operate
electric machine 18 in a manner to drive the bus current I_BP
substantially to zero. Specifically, block 118 calculates a q-axis
current vector Iqs_CMD based on the battery pack current error as
described above in reference to equation (1), and block 96
determines a d-axis current vector Ids_CMD by table look-up as a
function of Iqs_FB and machine speed. And block 98 then outputs the
current vector commands to the Current Controller 54 of FIG. 2.
Once I_BP is reduced below the threshold and block 106 is executed
to open the relay, block 116 will be answered in the affirmative,
triggering the execution of blocks 94-98 to operate electric
machine 18 for maintaining the bus voltage HV_BUS at the target
value HV_BUS_TAR, as described above in respect to the flow diagram
of FIG. 3.
[0026] In summary, the present invention provides a fast response
control methodology for safely and reliably disconnecting the
battery pack 20 from the high voltage bus 24 without having to
forego the generating capability of the electric machine 18,
thereby avoiding a walk-home condition, and maintaining normal
operation of the engine 10 and other vehicle electrical loads 38
until the engine 10 is turned off. While the control methodology
has been described in reference to the illustrated embodiment, it
should be understood that various modifications in addition to
those mentioned above will occur to persons skilled in the art.
Accordingly, it is intended that the invention not be limited to
the disclosed embodiment, but that it have the full scope permitted
by the language of the following claims.
* * * * *